The rotational motion of sickle hemoglobin in gels has been monitored by 13C NMR with new decoupling procedures as a probe of the gelation process upon deoxygenation. It has been possible to quantitate the degree of immobilization in gells from cell-free hemoglobin solutions, as well as the intracellular gelation or sickling process. In addition, theoretical analysis of the results of recent inhibition studies o the gelation by amino acids indicate that the inhibition may be due to direct, but very weak, binding between amino acids and hemoglobin. Detailed theoretical analyses of the disagreement between calorimetric and van't Hoff enthalpies of tubulin polymerization cast doubt upon the interpretation of many in vivo microtubule assembly studies. These analyses may be extended to include kinetic aspects of sickle hemoglobin gelation. BIBLIOGRAPHIC REFERENCE: Sutherland, J.W.H.: Disagreement Between Calorimetric and van't Hoff Enthalpies of Assembly of Protein Supramolecular Structures. Proc. Natl. Acad. Sci. 74: 2002-2006, 1977.